#include <stdio.h>
#include <math.h>

int main() {
    double x1, y1;
    double x2, y2;
    double distance;
    scanf("%lf%lf\n",&x1,&y1);
    scanf("%lf%lf",&x2,&y2);
    distance = sqrt(((x2-x1)*(x2-x1))+((y2-y1)*(y2-y1)));
    printf("%.4lf",distance);
    return 0;
}